When the nightmare started

I've been married for 25 years, I'm fat not good looking. I have very little self esteem and suffer with extreme pain every day. My wife on the other hand extremely good looking fit and takes care of herself at the gym each day. For a few years our marriage hasn't been good I think mainly due to my insecurities. We decided to buy a house in the Philippines to retire in as the heat helped so much with my pain. We made many friends well I have to say tbo my wife made lots of friends and I was friends by default even being made god father to one of her friends child. My wife always told me that there was many women that would try to temp western men and get husbands etc. I didn't take much notice
a. Because of how I was even I don't take interest in me let alone anyone else.
Ok this is the part I explain what happened and when the nightmare started.
Firstly I'm not asking for forgiveness and I fully expect to be stomped on. There is no excuse for what happened and I except that.
Ok I was out walking in the city when I came across my wife's friend and her child, she was loaded down with shopping and asked me if I could help take the shopping back to her house, I thought nothing of it, friend of the wife and me god father to her child etc so of course I said yes I didn't want to offend her. We got back to her house she said thank you and offered me a coffee which I excepted. Then when I was about to leave she pulled down my shorts and put my penis in her mouth. I didn't expect it but I was so weak instead of pushing her away and getting out of there I let it happen and of course it led to full intercourse. Although it was only like 15mins. It was done. I spent the next few hours wandering the streets knowing what happened and the guilt and shame I felt. Then the nightmare she contacted me asking for money...or I tell your wife. I love my wife very much, I know some will say if I did it wouldn't have happened. But I truly do. The requests for money got more frequent but I managed to avoid paying through many excuses this carried on for nearly 2years. When she didn't get a message from me she got angry and threatening at some points would ring 15 or more times over and over until I answered.
Every day I hid this from my wife scared of what would happen I didn't want to lose her. I even had to say things like I loved her and wanted to be with her. The only way to keep her from being angry. Well in the end my wife found out and saw naked pictures of the woman. She sent to me. Of course I destroyed her trust in me I lied about spending money because of how humiliating it was. And worst of all I had intercourse with another woman. I can't excuse what happened but I really don't want to lose my wife I really love her with all my heart. Something that has happened since all this came out our sex life has not stopped as you would imagine but the opposite it's gone way beyond it's ever been in 25yrs its passionate and very intimate and intense. Which is very confusing. What is happening. How can I try to fix this. Please help me I need to try to save my marriage